Re: ENERGY WITH Q

["Carl E. Mungan" <mungan@USNA.EDU>]

Ludwik wrote:

> In calorimetry heat is a form of energy. It is something that
> an object can either receive or loose, for example "by conduction."
> The naive fluid-like model of heat is later replaced by a better
> model (heat is a change in thermal molecular energy, or
> something equivalent). But in thermodynamics heat is not
> a form of energy.

Your middle sentence is the key point. You changed *models* of heat.
But the real calorimetric process couldn't care less about your
models. It was thermodynamics *before* you recognized it as such. A
rose by any other name....

My point is this:
In simple form, calorimetry involves two isolated objects A and B,
one of which has a higher temperature than the other. Hence energy is
transferred from one to the other. We call this "heat." Now take any
other thermodynamic process you like: ideal gases, sliding blocks,
muscles, whatever. In every case, look to see if two objects in
thermal contact (ie. not necessarily in physical contact) have
different temperatures. For simplicity, restrict attention only to
macroscopic objects and assume quasi-thermal-equilibrium, ie. all
processes occur slowly. First calculate the work by looking at the
forces between the objects. Next calculate the heat using the
equations for conduction and radiation; yes, do exactly what you did
in calorimetry - heck, use the same caloric model if you like. Sum
these heat and work terms together. This will equal the energy
transfer, ie. the energy gained by A and lost by B say.

Now granted, I made two big simplifying assumptions right in the
middle of the above paragraph. I leave it to David Bowman and others
to provide appropriate generalizations to the microscopic and
nonequilibrium cases.
--
Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
      U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu    http://physics.usna.edu/physics/faculty/mungan/